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This invention relates to a waste heat boiler for cooling hot synthesis gas (syngas).
Hot syngases such as those generated in oil or residue gasification plants, are cooled in a syngas waste heat boiler downstream from the gasification rector. The thermal energy of the syngas is recovered, producing high-pressure saturated steam. In order to serve a subsequent useful purpose, this saturated steam usually has to be superheated.
Syngas waste heat boilers for generating high-pressure saturated steam may consist of spiral-coiled tubes, for instance, or a bundle of straight or U-shaped tubes that form the heat-exchange surface. The hot syngas flows through these spiral-coiled tubes or tube bundles and releases its heat to the water, which is under boiling pressure and surround-the spiral-coiled tubes or tube bundles inside a pressure shell.
The saturated steam is superheated in a separate superheater downstream from the waste heat boiler. Also known are steam superheaters integrated into syngas waste heat boilers, which superheaters consist of spiral-coiled tubes installed downstream from the waste heat boiler coiled tubes, and in which the syngas flows through the coiled tubes in the same way it does in the waste heat boiler. As a rule, the superheater coiled tubes have a smaller tube diameter than the waste heat boiler coiled tubes. The saturated steam is conducted around the superheater coiled tubes, being superheated in the process. This design has the following serious disadvantages: It is inherently expensive and complex; it can only be inspected and repaired with considerable expenditures. The syngas flowing through the superheater coiled tube can cause deposits to form inside the coiled tube that lead to clogging, making the superheater ineffective. Due to the relatively small tube diameter, these occlusions are almost impossible to remove or only with great difficulty.
Furthermore, coiled-tube steam superheaters, integrated into syngas waste heat boilers, are known (Chem.-Ing.-Techn.56, 1984, Issue 5, pp. 356-360), in which the syngas is conducted around the coiled tubes, and the saturated steam to be superheated, through the coiled tubes. This integrated steam superheater is also expensive and complex and can only be inspected and repaired with considerable effort and expenditures. In addition, at least in the case of gasification of liquid feedstock, the flow channels between the coiled tubes become clogged by sediments from the syngas. These sediments cannot be removed and, after a certain period of time, render the superheater ineffective.
The goal of the invention is to integrate the superheater into the waste heat boiler in such a way as to create a simple and cost-effective design, where the superheater is relatively easy to inspect, to clean and to repair.